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添加应用内导航</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="tutorial/toh-pt6" title="第六部分：通过 HTTP 来获取并保存英雄数据。" target="_self"><span>6. 从服务器获取数据</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 expanded selected ng-star-inserted" title="通过数据绑定构建动态视图" aria-pressed="true"><span>组件与模板</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 expanded selected"><aio-nav-item class="ng-star-inserted"><div 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href="guide/lifecycle-hooks" title="Angular 调用指令和组件的生命周期钩子函数，包括它的创建、变更和销毁时。" target="_self"><span>生命周期钩子</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/component-interaction" title="在不同的指令和组件之间共享信息" target="_self"><span>组件交互</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/component-styles" title="添加专属于某个组件的样式" target="_self"><span>组件样式</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dynamic-component-loader" title="动态加载组件" target="_self"><span>动态组件</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/elements" title="把组件转换成自定义元素" target="_self"><span>Angular 元素</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/attribute-directives" title="属性型指令把行为添加到现有元素上。" target="_self"><span>属性型指令</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/structural-directives" title="结构型指令可以操纵页面的布局" target="_self"><span>结构型指令</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 expanded selected ng-star-inserted" style="position:relative" href="guide/pipes" title="管道可以在模板中转换显示的内容。" target="_self"><span>管道</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 的表单" aria-pressed="false"><span>表单</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/forms-overview" title="表单可以创建集中、高效、引人注目的输入体验。Angular 表单可以协调一组数据绑定控件，跟踪变更，验证输入，并表达错误信息。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/reactive-forms" title="使用 FormBuilder、表单组和表单数组创建响应式表单。" target="_self"><span>响应式表单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/forms" title="使用指令和 Angular 模板语法创建模板驱动表单。" target="_self"><span>模板驱动表单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/form-validation" title="验证用户的表单输入" target="_self"><span>表单验证</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dynamic-form" title="使用 FormGroup 渲染动态表单。" target="_self"><span>动态表单</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Observable 与 RxJS" aria-pressed="false"><span>Observable 与 RxJS</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/observables" title="" target="_self"><span>可观察对象(Observable)</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/rx-library" title="" target="_self"><span>RxJS 库</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/observables-in-angular" title="" target="_self"><span>Angular 中的可观察对象</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/practical-observable-usage" title="" target="_self"><span>用法实战</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/comparing-observables" title="" target="_self"><span>与其它技术的比较</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 中的模块" aria-pressed="false"><span>NgModules</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodules" title="使用 NgModule 让你的应用更高效" target="_self"><span>NgModule 简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-vs-jsmodule" title="JavaScript 模块和 NgModule 之间的差异" target="_self"><span>JS 模块 vs NgModule</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/bootstrapping" title="告诉 Angular 如何在根 &quot;AppModule&quot; 中构造和引导应用。" target="_self"><span>应用的根模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/frequent-ngmodules" title="介绍最常用的 NgModule" target="_self"><span>常用模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/module-types" title="介绍特性模块的几种类型" target="_self"><span>特性模块的分类</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/entry-components" title="关于 Angular 中入口组件的一切" target="_self"><span>入口组件</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/feature-modules" title="创建特性模块，以组织你的代码" target="_self"><span>特性模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/providers" title="服务提供者与 NgModule" target="_self"><span>服务提供者</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/singleton-services" title="创建单例服务" target="_self"><span>单例服务</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/lazy-loading-ngmodules" title="惰性加载模块，以提高应用的性能" target="_self"><span>惰性加载的特性模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/sharing-ngmodules" title="共享 NgModule 让你的应用现代化。" target="_self"><span>共享 NgModule</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-api" title="理解 NgModule 的那些细节。" target="_self"><span>NgModule API</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-faq" title="回答关于 NgModules 的常见问题。" target="_self"><span>NgModule 常见问题</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="依赖注入：创建并注入各种服务。" aria-pressed="false"><span>依赖注入</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection" title="Angular 的依赖注入系统能够为 Angular 创建的类创建并交付它们所依赖的服务。" target="_self"><span>Angular 依赖注入</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/hierarchical-dependency-injection" title="与组件树平行的注入器树，并支持嵌套的依赖。" target="_self"><span>多级注入器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-providers" title="各种提供者类型的更多知识。" target="_self"><span>DI 提供者</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-in-action" title="依赖注入的使用技巧" target="_self"><span>DI 实战</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-navtree" title="使用注入器树来查找父组件。" target="_self"><span>浏览组件树</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/http" title="通过 HTTP 协议与远程服务器对话。" target="_self"><span>HttpClient</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/router" title="揭示如何通过 Angular 路由进行基本的屏幕导航。" target="_self"><span>路由与导航</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 动画系统指南" aria-pressed="false"><span>动画</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/animations" title="Angular 动画的基础技术。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/transition-and-triggers" title="转场与触发器的高级技术。" target="_self"><span>转场与触发器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/complex-animation-sequences" title="复杂的 Angular 动画序列。" target="_self"><span>复杂序列</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/reusable-animations" title="创建可复用的动画。" target="_self"><span>可复用动画</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/route-animations" title="为路由提供转场动画。" target="_self"><span>路由转场动画</span></a></div></aio-nav-item></div></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="把 Angular 用到你的实际工作中的一些技巧" aria-pressed="false"><span>其它技术</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/security" title="Angular 应用开发中的安全技术。" target="_self"><span>安全</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/i18n" title="把应用模板中的文本翻译成多种语言。" target="_self"><span>国际化（i18n）</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/accessibility" title="设计能被所有用户访问的应用" target="_self"><span>无障碍（a11y）</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular Service Worker: 控制应用资源的缓存。" aria-pressed="false"><span>Service Worker 与 PWA</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-intro" title="Angular 对 Service Worker 的实现提升了慢速或不稳定的网络连接下的用户体验。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-getting-started" title="在 CLI 项目中启用 Service Worker，并在浏览器中查看效果。" target="_self"><span>快速上手</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/app-shell" title="在 CLI 项目中启用应用外壳。" target="_self"><span>应用外壳</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-communications" title="那些能让你和 Angular 的 Service Worker 通讯的服务类。" target="_self"><span>与 Service Worker 通讯</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-devops" title="使用 Service Worker 运行应用、管理应用更新、调试以及杀掉正在运行的应用。" target="_self"><span>生产环境下的 Service Worker</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-config" title="配置 Service Worker 的缓存行为。" target="_self"><span>Service Worker 配置</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/universal" title="使用 Angular Universal 在服务端渲染 HTML。" target="_self"><span>服务端渲染</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="把 AngularJS 应用增量式的升级到 Angular。" aria-pressed="false"><span>从 AngularJS 升级</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/upgrade" title="把 AngularJS 应用增量式的升级到 Angular。" target="_self"><span>升级步骤</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/upgrade-performance" title="用更灵活的方式把 AngularJS 升级到 Angular。" target="_self"><span>更关注性能的升级方式</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ajs-quick-reference" title="学习如何把 AngularJS 的概念映射到 Angular 中。" target="_self"><span>AngularJS 与 Angular 的概念对照</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="使用共享库扩展 Angular" aria-pressed="false"><span>开发 Angular 库</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/libraries" title="理解何时以及如何使用和创建库。" target="_self"><span>库概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/using-libraries" title="把已发布的库集成进你的应用中。" target="_self"><span>使用已发布的库</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/creating-libraries" title="通过创建、发布和使用你自己的库来扩展 Angular。" target="_self"><span>创建库</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="理解原理图" aria-pressed="false"><span>原理图（Schematic）</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics" title="理解 Angular 如何使用原理图。" target="_self"><span>原理图概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics-authoring" title="理解原理图的结构。" target="_self"><span>制作原理图</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics-for-libraries" title="使用原理图来把你的库集成进 Angular CLI 中。" target="_self"><span>库的原理图</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/cli-builder" title="使用构建器定制 Angular CLI。" target="_self"><span>CLI 构建器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/web-worker" title="在 Angular CLI 中使用 Web Worker。" target="_self"><span>Web Worker</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="关于构建、测试和部署的信息" aria-pressed="false"><span>开发工作流</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="理解 AOT 预先编译器。" aria-pressed="false"><span>AOT 预先编译器</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/aot-compiler" title="学习为何以及如何使用预先编译器。" target="_self"><span>预先编译</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/angular-compiler-options" title="配置 AOT 编译。" target="_self"><span>Angular 编译器选项</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/aot-metadata-errors" title="解决 AOT 编译错误。" target="_self"><span>AOT 元数据错误</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/template-typecheck" title="Angular 中的模板类型检查。" target="_self"><span>模板类型检查</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/build" title="构建应用及为应用启动开发服务器。" target="_self"><span>构建与运行</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/bazel" title="如何配置你的环境，以利用 Bazel 进行构建和测试。" target="_self"><span>使用 Bazel 进行构建</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/testing" title="测试 Angular 应用的技巧与实践。" target="_self"><span>测试</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/deployment" title="了解如何部署 Angular 应用。" target="_self"><span>发布</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="与开发环境和工具集成起来" aria-pressed="false"><span>开发工具集成</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/language-service" title="使用 Angular 语言服务加速开发。" target="_self"><span>语言服务</span></a></div></aio-nav-item></div></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="工作空间与项目的结构，及其配置文件。" aria-pressed="false"><span>配置</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/file-structure" title="Angular 工作区在文件系统中是怎样的。" target="_self"><span>项目文件结构</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/workspace-config" title="&quot;angular.json&quot; 包含供 CLI 命令使用的工作区和项目默认配置。" target="_self"><span>工作区配置</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/npm-packages" title="开发期间和运行期间所需的 npm 包的说明。" target="_self"><span>npm 包</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/typescript-configuration" title="给 Angular 开发者的 TypeScript 配置。" target="_self"><span>TypeScript 配置</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/browser-support" title="浏览器支持与腻子脚本指南。" target="_self"><span>浏览器支持</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular 的版本发布实践、更新与升级。" aria-pressed="false"><span>发布信息</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/updating" title="如何把 Angular 应用和库升级到最新版本。" target="_self"><span>保持最新</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/releases" title="Angular 的版本、发布、支持、弃用策略及实践。" target="_self"><span>发布实践</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/updating-to-version-9" title="支持把你的应用从 8 升级到 9。" target="_self"><span>升级到第 9 版</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/deprecations" title="弃用的 Angular API 和特性汇总。" target="_self"><span>弃用清单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/ivy" title="关于 Angular Ivy 的编译与渲染管道。" target="_self"><span>Angular Ivy</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular 语法、编码、术语汇总。" aria-pressed="false"><span>快捷手册</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/cheatsheet" title="关于 Angular 常用编码技术的快速指南。" target="_self"><span>速查表</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/styleguide" title="写出 Angular 风格的程序" target="_self"><span>风格指南</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/glossary" title="Angular 中最重要的词汇的简要定义。" target="_self"><span>词汇表</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular CLI 命令参考手册。" aria-pressed="false"><span>CLI 命令</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli" title="CLI 工具介绍、命令、语法" target="_self"><span>概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/usage-analytics-gathering" title="管理员如何从用户那里收集使用情况分析。" target="_self"><span>使用情况分析</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/add" title="ng add." target="_self"><span>ng add</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/analytics" title="ng analytics." target="_self"><span>ng analytics</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/build" title="ng build." target="_self"><span>ng build</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/config" title="ng config." target="_self"><span>ng config</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/deploy" title="ng deploy." target="_self"><span>ng deploy</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/doc" title="ng doc." target="_self"><span>ng doc</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/e2e" title="ng e2e." target="_self"><span>ng e2e</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/generate" title="ng generate." target="_self"><span>ng generate</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/help" title="ng help." target="_self"><span>ng help</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/lint" title="ng lint." target="_self"><span>ng lint</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/new" title="ng new." target="_self"><span>ng new</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/run" title="ng run." target="_self"><span>ng run</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/serve" title="ng serve." target="_self"><span>ng serve</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/test" title="ng test." target="_self"><span>ng test</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div 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ng-tns-c18-1"><aio-select><div class="form-select-menu"><button class="form-select-button"><span><strong></strong></span><span>stable (v9.0.0)</span></button></div></aio-select></div></div></mat-sidenav><div class="cdk-visually-hidden cdk-focus-trap-anchor" aria-hidden="true"></div><mat-sidenav-content cdkscrollable="" class="mat-drawer-content mat-sidenav-content ng-star-inserted" style="margin-left:261px"><main role="main" class="sidenav-content" id="guide-pipes"><aio-mode-banner></aio-mode-banner><aio-doc-viewer class=""><div style="opacity:1"><div class="github-links"><a href="https://github.com/angular/angular-cn/edit/aio/aio/content/guide/pipes.md?message=docs%3A%20请简述你的修改..." aria-label="提供编辑建议" title="提供编辑建议"><i class="material-icons" aria-hidden="true" role="img">mode_edit</i></a></div><div class="content"><h1 id="pipes" translation-result="on">管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pipes"><i class="material-icons">link</i></a></h1><aio-toc class="embedded" ng-version="9.0.0-rc.11"><div class="toc-inner no-print collapsed ng-star-inserted"><button type="button" title="Expand/collapse contents" aria-label="Expand/collapse contents" class="toc-heading embedded secondary ng-star-inserted" aria-pressed="false">目录<mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon collapsed mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><ul class="toc-list embedded"><li class="h2 ng-star-inserted" title="使用管道"><a href="guide/pipes#using-pipes">使用管道</a></li><li class="h2 ng-star-inserted" title="内置的管道"><a href="guide/pipes#built-in-pipes">内置的管道</a></li><li class="h2 ng-star-inserted" title="对管道进行参数化"><a href="guide/pipes#parameterizing-a-pipe">对管道进行参数化</a></li><li class="h2 secondary ng-star-inserted" title="链式管道"><a href="guide/pipes#chaining-pipes">链式管道</a></li><li class="h2 secondary ng-star-inserted" title="自定义管道"><a href="guide/pipes#custom-pipes">自定义管道</a></li><li class="h2 secondary ng-star-inserted" title="PipeTransform 接口"><a href="guide/pipes#the-pipetransform-interface"><em>PipeTransform</em> 接口</a></li><li class="h2 secondary ng-star-inserted" title="能力倍增计算器"><a href="guide/pipes#power-boost-calculator">能力倍增计算器</a></li><li class="h2 secondary ng-star-inserted" title="管道与变更检测"><a href="guide/pipes#pipes-and-change-detection">管道与变更检测</a></li><li class="h2 secondary ng-star-inserted" title="纯(pure)管道与非纯(impure)管道"><a href="guide/pipes#pure-and-impure-pipes">纯(pure)管道与非纯(impure)管道</a></li><li class="h2 secondary ng-star-inserted" title="下一步"><a href="guide/pipes#next-steps">下一步</a></li><li class="h2 secondary ng-star-inserted" title="附录：没有 FilterPipe 或者 OrderByPipe"><a href="guide/pipes#appendix-no-filterpipe-or-orderbypipe">附录：没有 <em>FilterPipe</em> 或者 <em>OrderByPipe</em></a></li></ul><button type="button" title="Expand/collapse contents" aria-label="Expand/collapse contents" class="toc-more-items embedded material-icons collapsed ng-star-inserted" aria-pressed="false"></button></div></aio-toc><h1 translation-origin="off" id="pipes">Pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pipes"><i class="material-icons">link</i></a></h1><p translation-result="on">每个应用开始的时候差不多都是一些简单任务：获取数据、转换它们，然后把它们显示给用户。 获取数据可能简单到创建一个局部变量就行，也可能复杂到从 WebSocket 中获取数据流。</p><p translation-origin="off">Every application starts out with what seems like a simple task: get data, transform them, and show them to users. Getting data could be as simple as creating a local variable or as complex as streaming data over a WebSocket.</p><p translation-result="on">一旦取到数据，你就可以把它们原始值的 <code>toString</code> 结果直接推入视图中。 但这种做法很少能具备良好的用户体验。 比如，几乎每个人都更喜欢简单的日期格式，例如<samp>1988-04-15</samp>，而不是服务端传过来的原始字符串格式 —— <samp>Fri Apr 15 1988 00:00:00 GMT-0700 (Pacific Daylight Time)</samp>。</p><p translation-origin="off">Once data arrives, you could push their raw <code>toString</code> values directly to the view, but that rarely makes for a good user experience. For example, in most use cases, users prefer to see a date in a simple format like <samp>April 15, 1988</samp> rather than the raw string format <samp>Fri Apr 15 1988 00:00:00 GMT-0700 (Pacific Daylight Time)</samp>.</p><p translation-result="on">显然，有些值最好显示成用户友好的格式。你很快就会发现，在很多不同的应用中，都在重复做出某些相同的变换。 你几乎会把它们看做某种 CSS 样式，事实上，你也确实更喜欢在 HTML 模板中应用它们 —— 就像 CSS 样式一样。</p><p translation-origin="off">Clearly, some values benefit from a bit of editing. You may notice that you desire many of the same transformations repeatedly, both within and across many applications. You can almost think of them as styles. In fact, you might like to apply them in your HTML templates as you do styles.</p><p translation-result="on">通过引入 Angular 管道（一种编写"从显示到值"转换逻辑的途径），你可以把它声明在 HTML 中。</p><p translation-origin="off">Introducing Angular pipes, a way to write display-value transformations that you can declare in your HTML.</p><p translation-result="on">你可以运行<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>，在 Stackblitz 中试用并下载本页的代码。</p><p translation-origin="off">You can run the<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>in Stackblitz and download the code from there.</p><h2 id="using-pipes" translation-result="on">使用管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#using-pipes"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="using-pipes">Using pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#using-pipes"><i class="material-icons">link</i></a></h2><p translation-result="on">管道把数据作为输入，然后转换它，给出期望的输出。 你要把组件的 <code>birthday</code> 属性转换成对人类更友好的日期格式。</p><p translation-origin="off">A pipe takes in data as input and transforms it to a desired output. In this page, you'll use pipes to transform a component's birthday property into a human-friendly date.</p><code-example path="pipes/src/app/hero-birthday1.component.ts" header="src/app/hero-birthday1.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Component" class="code-anchor">Component</a> } from '@angular/core'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-hero-birthday', template: `&lt;p&gt;The hero's birthday is {{ birthday | <a href="api/common/DatePipe" class="code-anchor">date</a> }}&lt;/p&gt;` }) export class HeroBirthdayComponent { birthday = new Date(1988, 3, 15); // April 15, 1988 }</div><header class="ng-star-inserted">src/app/hero-birthday1.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero-birthday1.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Component" class="code-anchor"><span class="typ">Component</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-hero-birthday'</span><span class="pun">,</span><span class="pln">
  </span><span class="kwd">template</span><span class="pun">:</span><span class="pln"> </span><span class="str">`&lt;p&gt;The hero's birthday is {{ birthday | </span><a href="api/common/DatePipe" class="code-anchor"><span class="str">date</span></a><span class="str"> }}&lt;/p&gt;`</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroBirthdayComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  birthday </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Date</span><span class="pun">(</span><span class="lit">1988</span><span class="pun">,</span><span class="pln"> </span><span class="lit">3</span><span class="pun">,</span><span class="pln"> </span><span class="lit">15</span><span class="pun">);</span><span class="pln"> </span><span class="com">// April 15, 1988</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">重点看下组件的模板。</p><p translation-origin="off">Focus on the component's template.</p><code-example path="pipes/src/app/app.component.html" region="hero-birthday-template" header="src/app/app.component.html" ng-version="9.0.0-rc.11"><div style="display:none">&lt;p&gt;The hero's birthday is {{ birthday | <a href="api/common/DatePipe" class="code-anchor">date</a> }}&lt;/p&gt;</div><header class="ng-star-inserted">src/app/app.component.html</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/app.component.html">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="tag">&lt;p&gt;</span><span class="pln">The hero's birthday is {{ birthday | </span><a href="api/common/DatePipe" class="code-anchor"><span class="pln">date</span></a><span class="pln"> }}</span><span class="tag">&lt;/p&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">在这个插值表达式中，你让组件的 <code>birthday</code> 值通过<a href="guide/template-syntax#pipe">管道操作符</a>( | )流动到 右侧的<a href="api/common/DatePipe">Date 管道</a>函数中。所有管道都会用这种方式工作。</p><p translation-origin="off">Inside the interpolation expression, you flow the component's <code>birthday</code> value through the <a href="guide/template-syntax#pipe">pipe operator</a> ( | ) to the <a href="api/common/DatePipe">Date pipe</a> function on the right. All pipes work this way.</p><h2 id="built-in-pipes" translation-result="on">内置的管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#built-in-pipes"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="built-in-pipes">Built-in pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#built-in-pipes"><i class="material-icons">link</i></a></h2><p translation-result="on">Angular 内置了一些管道，比如 <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code>、<code><a href="api/common/UpperCasePipe" class="code-anchor">UpperCasePipe</a></code>、<code><a href="api/common/LowerCasePipe" class="code-anchor">LowerCasePipe</a></code>、<code><a href="api/common/CurrencyPipe" class="code-anchor">CurrencyPipe</a></code> 和 <code><a href="api/common/PercentPipe" class="code-anchor">PercentPipe</a></code>。 它们全都可以直接用在任何模板中。</p><p translation-origin="off">Angular comes with a stock of pipes such as <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code>, <code><a href="api/common/UpperCasePipe" class="code-anchor">UpperCasePipe</a></code>, <code><a href="api/common/LowerCasePipe" class="code-anchor">LowerCasePipe</a></code>, <code><a href="api/common/CurrencyPipe" class="code-anchor">CurrencyPipe</a></code>, and <code><a href="api/common/PercentPipe" class="code-anchor">PercentPipe</a></code>. They are all available for use in any template.</p><div class="alert is-helpful"><p translation-result="on">要学习更多内置管道的知识，参见<a href="api?type=pipe">API 参考手册</a>，并用“pipe”为关键词对结果进行过滤。</p><p translation-origin="off">Read more about these and many other built-in pipes in the <a href="api?type=pipe">pipes topics</a> of the <a href="api">API Reference</a>; filter for entries that include the word "pipe".</p><p translation-result="on">Angular 没有 <code>FilterPipe</code> 或 <code>OrderByPipe</code> 管道，原因在<a href="guide/pipes#no-filter-pipe">后面的附录中</a>有解释。</p><p translation-origin="off">Angular doesn't have a <code>FilterPipe</code> or an <code>OrderByPipe</code> for reasons explained in the <a href="guide/pipes#no-filter-pipe">Appendix</a> of this page.</p></div><h2 id="parameterizing-a-pipe" translation-result="on">对管道进行参数化<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#parameterizing-a-pipe"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="parameterizing-a-pipe">Parameterizing a pipe<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#parameterizing-a-pipe"><i class="material-icons">link</i></a></h2><p translation-result="on">管道可能接受任何数量的可选参数来对它的输出进行微调。 可以在管道名后面添加一个冒号( : )再跟一个参数值，来为管道添加参数(比如 <code>currency:'EUR'</code>)。 如果这个管道可以接受多个参数，那么就用冒号来分隔这些参数值(比如 <code>slice:1:5</code>)。</p><p translation-origin="off">A pipe can accept any number of optional parameters to fine-tune its output. To add parameters to a pipe, follow the pipe name with a colon ( : ) and then the parameter value (such as <code>currency:'EUR'</code>). If the pipe accepts multiple parameters, separate the values with colons (such as <code>slice:1:5</code>)</p><p translation-result="on">修改生日模板，来为这个日期管道提供一个格式化参数。 当格式化完该英雄的 4 月 15 日生日之后，它应该被渲染成<strong><samp>04/15/88</samp></strong>。</p><p translation-origin="off">Modify the birthday template to give the date pipe a format parameter. After formatting the hero's April 15th birthday, it renders as <strong><samp>04/15/88</samp></strong>:</p><code-example path="pipes/src/app/app.component.html" region="format-birthday" header="src/app/app.component.html" ng-version="9.0.0-rc.11"><div style="display:none">&lt;p&gt;The hero's birthday is {{ birthday | <a href="api/common/DatePipe" class="code-anchor">date</a>:"MM/dd/yy" }} &lt;/p&gt;</div><header class="ng-star-inserted">src/app/app.component.html</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/app.component.html">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="tag">&lt;p&gt;</span><span class="pln">The hero's birthday is {{ birthday | </span><a href="api/common/DatePipe" class="code-anchor"><span class="pln">date</span></a><span class="pln">:"MM/dd/yy" }} </span><span class="tag">&lt;/p&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">参数值可以是任何有效的模板表达式（参见<a href="guide/template-syntax">模板语法</a>中的<a href="guide/template-syntax#template-expressions">模板表达式</a>部分），比如字符串字面量或组件的属性。 换句话说，借助属性绑定，你也可以像用绑定来控制生日的值一样，控制生日的显示格式。</p><p translation-origin="off">The parameter value can be any valid template expression, (see the <a href="guide/template-syntax#template-expressions">Template expressions</a> section of the <a href="guide/template-syntax">Template Syntax</a> page) such as a string literal or a component property. In other words, you can control the format through a binding the same way you control the birthday value through a binding.</p><p translation-result="on">来写第二个组件，它把管道的格式参数<em>绑定</em>到该组件的 <code>format</code> 属性。这里是新组件的模板：</p><p translation-origin="off">Write a second component that <em>binds</em> the pipe's format parameter to the component's <code>format</code> property. Here's the template for that component:</p><code-example path="pipes/src/app/hero-birthday2.component.ts" region="template" header="src/app/hero-birthday2.component.ts (template)" ng-version="9.0.0-rc.11"><div style="display:none">template: ` &lt;p&gt;The hero's birthday is {{ birthday | <a href="api/common/DatePipe" class="code-anchor">date</a>:format }}&lt;/p&gt; &lt;button (click)="toggleFormat()"&gt;Toggle <a href="api/common/FormStyle#Format" class="code-anchor">Format</a>&lt;/button&gt; `</div><header class="ng-star-inserted">src/app/hero-birthday2.component.ts (template)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero-birthday2.component.ts (template)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">template</span><span class="pun">:</span><span class="pln"> </span><span class="str">`
  &lt;p&gt;The hero's birthday is {{ birthday | </span><a href="api/common/DatePipe" class="code-anchor"><span class="str">date</span></a><span class="str">:format }}&lt;/p&gt;
  &lt;button (click)="toggleFormat()"&gt;Toggle </span><a href="api/common/FormStyle#Format" class="code-anchor"><span class="str">Format</span></a><span class="str">&lt;/button&gt;
`</span></code>
    </pre></aio-code></code-example><p translation-result="on">你还能在模板中添加一个按钮，并把它的点击事件绑定到组件的 <code>toggleFormat()</code> 方法。 此方法会在短日期格式(<code>'shortDate'</code>)和长日期格式(<code>'fullDate'</code>)之间切换组件的 <code>format</code> 属性。</p><p translation-origin="off">You also added a button to the template and bound its click event to the component's <code>toggleFormat()</code> method. That method toggles the component's <code>format</code> property between a short form (<code>'shortDate'</code>) and a longer form (<code>'fullDate'</code>).</p><code-example path="pipes/src/app/hero-birthday2.component.ts" region="class" header="src/app/hero-birthday2.component.ts (class)" ng-version="9.0.0-rc.11"><div style="display:none">export class HeroBirthday2Component { birthday = new Date(1988, 3, 15); // April 15, 1988 toggle = true; // start with true == shortDate get format() { return this.toggle ? 'shortDate' : 'fullDate'; } toggleFormat() { this.toggle = !this.toggle; } }</div><header class="ng-star-inserted">src/app/hero-birthday2.component.ts (class)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero-birthday2.component.ts (class)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroBirthday2Component</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  birthday </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Date</span><span class="pun">(</span><span class="lit">1988</span><span class="pun">,</span><span class="pln"> </span><span class="lit">3</span><span class="pun">,</span><span class="pln"> </span><span class="lit">15</span><span class="pun">);</span><span class="pln"> </span><span class="com">// April 15, 1988</span><span class="pln">
  toggle </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">true</span><span class="pun">;</span><span class="pln"> </span><span class="com">// start with true == shortDate</span><span class="pln">

  </span><span class="kwd">get</span><span class="pln"> format</span><span class="pun">()</span><span class="pln">   </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">return</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">toggle </span><span class="pun">?</span><span class="pln"> </span><span class="str">'shortDate'</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="str">'fullDate'</span><span class="pun">;</span><span class="pln"> </span><span class="pun">}</span><span class="pln">
  toggleFormat</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">toggle </span><span class="pun">=</span><span class="pln"> </span><span class="pun">!</span><span class="kwd">this</span><span class="pun">.</span><span class="pln">toggle</span><span class="pun">;</span><span class="pln"> </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">当你点击此按钮的时候，所显示的日期会在“<strong><samp>04/15/1988</samp></strong>”和“<strong><samp>Friday, April 15, 1988</samp></strong>”之间切换。</p><p translation-origin="off">As you click the button, the displayed date alternates between "<strong><samp>04/15/1988</samp></strong>" and "<strong><samp>Friday, April 15, 1988</samp></strong>".</p><div class="lightbox"><img src="generated/images/guide/pipes/date-format-toggle-anim.gif" alt="Date Format Toggle" width="300" height="62"></div><div class="alert is-helpful"><p translation-result="on">要了解更多 <code>DatePipes</code> 的格式选项，请参阅<a href="api/common/DatePipe">API 文档</a>。</p><p translation-origin="off">Read more about the <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code> format options in the <a href="api/common/DatePipe">Date Pipe</a> API Reference page.</p></div><h2 id="chaining-pipes" translation-result="on">链式管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#chaining-pipes"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="chaining-pipes">Chaining pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#chaining-pipes"><i class="material-icons">link</i></a></h2><p translation-result="on">你可以把管道串联在一起，以组合出一些潜在的有用功能。 下面这个例子中，要把 <code>birthday</code> 串联到 <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code> 管道，然后又串联到 <code><a href="api/common/UpperCasePipe" class="code-anchor">UpperCasePipe</a></code>，这样就可以把生日显示成大写形式了。 生日被显示成了<strong><samp>APR 15, 1988</samp></strong>：</p><p translation-origin="off">You can chain pipes together in potentially useful combinations. In the following example, to display the birthday in uppercase, the birthday is chained to the <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code> and on to the <code><a href="api/common/UpperCasePipe" class="code-anchor">UpperCasePipe</a></code>. The birthday displays as <strong><samp>APR 15, 1988</samp></strong>.</p><code-example path="pipes/src/app/app.component.html" region="chained-birthday" header="src/app/app.component.html" ng-version="9.0.0-rc.11"><div style="display:none">The chained hero's birthday is {{ birthday | <a href="api/common/DatePipe" class="code-anchor">date</a> | <a href="api/common/UpperCasePipe" class="code-anchor">uppercase</a>}}</div><header class="ng-star-inserted">src/app/app.component.html</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/app.component.html">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="typ">The</span><span class="pln"> chained hero</span><span class="str">'s birthday is
{{ birthday | </span><a href="api/common/DatePipe" class="code-anchor"><span class="str">date</span></a><span class="str"> | </span><a href="api/common/UpperCasePipe" class="code-anchor"><span class="str">uppercase</span></a><span class="str">}}</span></code>
    </pre></aio-code></code-example><p translation-result="on">下面这个显示<strong><samp>FRIDAY, APRIL 15, 1988</samp></strong>的例子用同样的方式链接了这两个管道，而且同时还给 <code><a href="api/common/DatePipe" class="code-anchor">date</a></code> 管道传进去一个参数。</p><p translation-origin="off">This example—which displays <strong><samp>FRIDAY, APRIL 15, 1988</samp></strong>—chains the same pipes as above, but passes in a parameter to <code><a href="api/common/DatePipe" class="code-anchor">date</a></code> as well.</p><code-example path="pipes/src/app/app.component.html" region="chained-parameter-birthday" header="src/app/app.component.html" ng-version="9.0.0-rc.11"><div style="display:none">The chained hero's birthday is {{ birthday | <a href="api/common/DatePipe" class="code-anchor">date</a>:'fullDate' | uppercase}}</div><header class="ng-star-inserted">src/app/app.component.html</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/app.component.html">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="typ">The</span><span class="pln"> chained hero</span><span class="str">'s birthday is
{{  birthday | </span><a href="api/common/DatePipe" class="code-anchor"><span class="str">date</span></a><span class="str">:'</span><span class="pln">fullDate</span><span class="str">' | uppercase}}</span></code>
    </pre></aio-code></code-example><h2 id="custom-pipes" translation-result="on">自定义管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#custom-pipes"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="custom-pipes">Custom pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#custom-pipes"><i class="material-icons">link</i></a></h2><p translation-result="on">你还可以写自己的自定义管道。 下面就是一个名叫 <code>ExponentialStrengthPipe</code> 的管道，它可以放大英雄的能力：</p><p translation-origin="off">You can write your own custom pipes. Here's a custom pipe named <code>ExponentialStrengthPipe</code> that can boost a hero's powers:</p><code-example path="pipes/src/app/exponential-strength.pipe.ts" header="src/app/exponential-strength.pipe.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Pipe" class="code-anchor">Pipe</a>, <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> } from '@angular/core'; /* * Raise the value exponentially * Takes an exponent argument that defaults to 1. * Usage: * value | exponentialStrength:exponent * Example: * {{ 2 | exponentialStrength:10 }} * formats to: 1024 */ @<a href="api/core/Pipe" class="code-anchor">Pipe</a>({name: 'exponentialStrength'}) export class ExponentialStrengthPipe implements <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> { transform(value: number, exponent?: number): number { return Math.pow(value, isNaN(exponent) ? 1 : exponent); } }</div><header class="ng-star-inserted">src/app/exponential-strength.pipe.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/exponential-strength.pipe.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Pipe" class="code-anchor"><span class="typ">Pipe</span></a><span class="pun">,</span><span class="pln"> </span><a href="api/core/PipeTransform" class="code-anchor"><span class="typ">PipeTransform</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">
</span><span class="com">/*
 * Raise the value exponentially
 * Takes an exponent argument that defaults to 1.
 * Usage:
 *   value | exponentialStrength:exponent
 * Example:
 *   {{ 2 | exponentialStrength:10 }}
 *   formats to: 1024
*/</span><span class="pln">
</span><span class="lit">@</span><a href="api/core/Pipe" class="code-anchor"><span class="lit">Pipe</span></a><span class="pun">({</span><span class="pln">name</span><span class="pun">:</span><span class="pln"> </span><span class="str">'exponentialStrength'</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">ExponentialStrengthPipe</span><span class="pln"> </span><span class="kwd">implements</span><span class="pln"> </span><a href="api/core/PipeTransform" class="code-anchor"><span class="typ">PipeTransform</span></a><span class="pln"> </span><span class="pun">{</span><span class="pln">
  transform</span><span class="pun">(</span><span class="kwd">value</span><span class="pun">:</span><span class="pln"> number</span><span class="pun">,</span><span class="pln"> exponent</span><span class="pun">?:</span><span class="pln"> number</span><span class="pun">):</span><span class="pln"> number </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">return</span><span class="pln"> </span><span class="typ">Math</span><span class="pun">.</span><span class="pln">pow</span><span class="pun">(</span><span class="kwd">value</span><span class="pun">,</span><span class="pln"> isNaN</span><span class="pun">(</span><span class="pln">exponent</span><span class="pun">)</span><span class="pln"> </span><span class="pun">?</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> exponent</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">在这个管道的定义中体现了几个关键点：</p><p translation-origin="off">This pipe definition reveals the following key points:</p><ul><li><p translation-result="on">管道是一个带有“管道元数据(pipe metadata)”装饰器的类。</p><p translation-origin="off">A pipe is a class decorated with pipe metadata.</p></li><li><p translation-result="on">这个管道类实现了 <code><a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a></code> 接口的 <code>transform</code> 方法，该方法接受一个输入值和一些可选参数，并返回转换后的值。</p><p translation-origin="off">The pipe class implements the <code><a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a></code> interface's <code>transform</code> method that accepts an input value followed by optional parameters and returns the transformed value.</p></li><li><p translation-result="on">当每个输入值被传给 <code>transform</code> 方法时，还会带上另一个参数，比如你这个管道就有一个 <code>exponent</code>(放大指数) 参数。</p><p translation-origin="off">There will be one additional argument to the <code>transform</code> method for each parameter passed to the pipe. Your pipe has one such parameter: the <code>exponent</code>.</p></li><li><p translation-result="on">可以通过 <code>@<a href="api/core/Pipe" class="code-anchor">Pipe</a></code> 装饰器来告诉 Angular：这是一个管道。该装饰器是从 Angular 的 <code>core</code> 库中引入的。</p><p translation-origin="off">To tell Angular that this is a pipe, you apply the <code>@<a href="api/core/Pipe" class="code-anchor">Pipe</a></code> decorator, which you import from the core Angular library.</p></li><li><p translation-result="on">这个 <code>@<a href="api/core/Pipe" class="code-anchor">Pipe</a></code> 装饰器允许你定义管道的名字，这个名字会被用在模板表达式中。它必须是一个有效的 JavaScript 标识符。 比如，你这个管道的名字是 <code>exponentialStrength</code>。</p><p translation-origin="off">The <code>@<a href="api/core/Pipe" class="code-anchor">Pipe</a></code> decorator allows you to define the pipe name that you'll use within template expressions. It must be a valid JavaScript identifier. Your pipe's name is <code>exponentialStrength</code>.</p></li></ul><div class="alert is-helpful"><h2 id="the-pipetransform-interface" translation-result="on"><em>PipeTransform</em> 接口<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#the-pipetransform-interface"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="the-pipetransform-interface">The <em>PipeTransform</em> interface<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#the-pipetransform-interface"><i class="material-icons">link</i></a></h2><p translation-result="on"><code>transform</code> 方法是管道的基本要素。 <code><a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a></code><em>接口</em>中定义了它，并用它指导各种工具和编译器。 理论上说，它是可选的。Angular 不会管它，而是直接查找并执行 <code>transform</code> 方法。</p><p translation-origin="off">The <code>transform</code> method is essential to a pipe. The <code><a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a></code> <em>interface</em> defines that method and guides both tooling and the compiler. Technically, it's optional; Angular looks for and executes the <code>transform</code> method regardless.</p></div><p translation-result="on">现在，你需要一个组件来演示这个管道。</p><p translation-origin="off">Now you need a component to demonstrate the pipe.</p><code-example path="pipes/src/app/power-booster.component.ts" header="src/app/power-booster.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Component" class="code-anchor">Component</a> } from '@angular/core'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-power-booster', template: ` &lt;h2&gt;Power Booster&lt;/h2&gt; &lt;p&gt;Super power boost: {{2 | exponentialStrength: 10}}&lt;/p&gt; ` }) export class PowerBoosterComponent { }</div><header class="ng-star-inserted">src/app/power-booster.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/power-booster.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Component" class="code-anchor"><span class="typ">Component</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-power-booster'</span><span class="pun">,</span><span class="pln">
  </span><span class="kwd">template</span><span class="pun">:</span><span class="pln"> </span><span class="str">`
    &lt;h2&gt;Power Booster&lt;/h2&gt;
    &lt;p&gt;Super power boost: {{2 | exponentialStrength: 10}}&lt;/p&gt;
  `</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">PowerBoosterComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span></code>
    </pre></aio-code></code-example><div class="lightbox"><img src="generated/images/guide/pipes/power-booster.png" alt="Power Booster" width="300" height="105"></div><p translation-result="on">请注意以下几点：</p><p translation-origin="off">Note the following:</p><ul><li><p translation-result="on">你使用自定义管道的方式和内置管道完全相同。</p><p translation-origin="off">You use your custom pipe the same way you use built-in pipes.</p></li><li><p translation-result="on">你必须把这个管道添加到 <code>AppModule</code> 的 <code>declarations</code> 数组中。</p><p translation-origin="off">You must include your pipe in the <code>declarations</code> array of the <code>AppModule</code></p></li><li><p translation-result="on">如果选择将管道注入(<code>inject</code>)类中，则必须将管道包含字在<code><a href="api/core/NgModule" class="code-anchor">NgModule</a></code>的<code>providers</code>数组中。</p><p translation-origin="off">If you choose to inject your pipe into a class, you must provide it in the <code>providers</code> array of your <code><a href="api/core/NgModule" class="code-anchor">NgModule</a></code>.</p></li></ul><div class="callout is-helpful"><header translation-result="on">别忘了 `declarations` 数组</header><header translation-origin="off">Remember the declarations array</header><p translation-result="on">你必须手动注册自定义管道。如果忘了，Angular 就会报告一个错误。 在前一个例子中你没有把 <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code> 列进去，这是因为 Angular 所有的内置管道都已经预注册过了。</p><p translation-origin="off">You must register custom pipes. If you don't, Angular reports an error. The <a href="cli">Angular CLI's</a> generator registers the pipe automatically.</p></div><p translation-result="on">试一下这个<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>，并通过修改值和模板中的可选部分来体会其行为。</p><p translation-origin="off">To probe the behavior in the<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>, change the value and optional exponent in the template.</p><h2 id="power-boost-calculator" translation-result="on">能力倍增计算器<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#power-boost-calculator"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="power-boost-calculator">Power Boost Calculator<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#power-boost-calculator"><i class="material-icons">link</i></a></h2><p translation-result="on">仅仅升级模板来测试这个自定义管道其实没多大意思。 干脆把这个例子升级为“能力提升计算器”，它可以把该管道和使用 <code><a href="api/forms/NgModel" class="code-anchor">ngModel</a></code> 的双向数据绑定组合起来。</p><p translation-origin="off">It's not much fun updating the template to test the custom pipe. Upgrade the example to a "Power Boost Calculator" that combines your pipe and two-way data binding with <code><a href="api/forms/NgModel" class="code-anchor">ngModel</a></code>.</p><code-example path="pipes/src/app/power-boost-calculator.component.ts" header="src/app/power-boost-calculator.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Component" class="code-anchor">Component</a> } from '@angular/core'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-power-boost-calculator', template: ` &lt;h2&gt;Power Boost Calculator&lt;/h2&gt; &lt;div&gt;Normal power: &lt;input [(<a href="api/forms/NgModel" class="code-anchor">ngModel</a>)]="power"&gt;&lt;/div&gt; &lt;div&gt;Boost factor: &lt;input [(<a href="api/forms/NgModel" class="code-anchor">ngModel</a>)]="factor"&gt;&lt;/div&gt; &lt;p&gt; Super Hero Power: {{power | exponentialStrength: factor}} &lt;/p&gt; ` }) export class PowerBoostCalculatorComponent { power = 5; factor = 1; }</div><header class="ng-star-inserted">src/app/power-boost-calculator.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/power-boost-calculator.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Component" class="code-anchor"><span class="typ">Component</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-power-boost-calculator'</span><span class="pun">,</span><span class="pln">
  </span><span class="kwd">template</span><span class="pun">:</span><span class="pln"> </span><span class="str">`
    &lt;h2&gt;Power Boost Calculator&lt;/h2&gt;
    &lt;div&gt;Normal power: &lt;input [(</span><a href="api/forms/NgModel" class="code-anchor"><span class="str">ngModel</span></a><span class="str">)]="power"&gt;&lt;/div&gt;
    &lt;div&gt;Boost factor: &lt;input [(</span><a href="api/forms/NgModel" class="code-anchor"><span class="str">ngModel</span></a><span class="str">)]="factor"&gt;&lt;/div&gt;
    &lt;p&gt;
      Super Hero Power: {{power | exponentialStrength: factor}}
    &lt;/p&gt;
  `</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">PowerBoostCalculatorComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  power </span><span class="pun">=</span><span class="pln"> </span><span class="lit">5</span><span class="pun">;</span><span class="pln">
  factor </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><div class="lightbox"><img src="generated/images/guide/pipes/power-boost-calculator-anim.gif" alt="Power Boost Calculator" width="296" height="136"></div><a id="change-detection"></a><h2 id="pipes-and-change-detection" translation-result="on">管道与变更检测<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pipes-and-change-detection"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="pipes-and-change-detection">Pipes and change detection<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pipes-and-change-detection"><i class="material-icons">link</i></a></h2><p translation-result="on">Angular 通过<em>变更检测</em>过程来查找绑定值的更改，并在每一次 JavaScript 事件之后运行：每次按键、鼠标移动、定时器以及服务器的响应。 这可能会让变更检测显得很昂贵，但是 Angular 会尽可能降低变更检测的成本。</p><p translation-origin="off">Angular looks for changes to data-bound values through a <em>change detection</em> process that runs after every DOM event: every keystroke, mouse move, timer tick, and server response. This could be expensive. Angular strives to lower the cost whenever possible and appropriate.</p><p translation-result="on">当使用管道时，Angular 会选用一种更简单、更快速的变更检测算法。</p><p translation-origin="off">Angular picks a simpler, faster change detection algorithm when you use a pipe.</p><h3 class="no-toc" id="no-pipe" translation-result="on">无管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#no-pipe"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="no-pipe">No pipe<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#no-pipe"><i class="material-icons">link</i></a></h3><p translation-result="on">在下一个例子中，组件使用默认的、激进(昂贵)的变更检测策略来检测和更新 <code>heroes</code> 数组中的每个英雄。下面是它的模板：</p><p translation-origin="off">In the next example, the component uses the default, aggressive change detection strategy to monitor and update its display of every hero in the <code>heroes</code> array. Here's the template:</p><code-example path="pipes/src/app/flying-heroes.component.html" region="template-1" header="src/app/flying-heroes.component.html (v1)" ng-version="9.0.0-rc.11"><div style="display:none">New hero: &lt;input type="text" #box (keyup.enter)="addHero(box.value); box.value=''" placeholder="hero name"&gt; &lt;button (click)="reset()"&gt;Reset&lt;/button&gt; &lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>="let hero of heroes"&gt; {{hero.name}} &lt;/div&gt;</div><header class="ng-star-inserted">src/app/flying-heroes.component.html (v1)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.component.html (v1)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="typ">New</span><span class="pln"> hero</span><span class="pun">:</span><span class="pln">
  </span><span class="pun">&lt;</span><span class="pln">input type</span><span class="pun">=</span><span class="str">"text"</span><span class="pln"> </span><span class="com">#box</span><span class="pln">
          </span><span class="pun">(</span><span class="pln">keyup</span><span class="pun">.</span><span class="pln">enter</span><span class="pun">)=</span><span class="str">"addHero(box.value); box.value=''"</span><span class="pln">
          placeholder</span><span class="pun">=</span><span class="str">"hero name"</span><span class="pun">&gt;</span><span class="pln">
  </span><span class="pun">&lt;</span><span class="pln">button </span><span class="pun">(</span><span class="pln">click</span><span class="pun">)=</span><span class="str">"reset()"</span><span class="pun">&gt;</span><span class="typ">Reset</span><span class="pun">&lt;/</span><span class="pln">button</span><span class="pun">&gt;</span><span class="pln">
  </span><span class="pun">&lt;</span><span class="pln">div </span><span class="pun">*</span><a href="api/common/NgForOf" class="code-anchor"><span class="pln">ngFor</span></a><span class="pun">=</span><span class="str">"let hero of heroes"</span><span class="pun">&gt;</span><span class="pln">
    </span><span class="pun">{{</span><span class="pln">hero</span><span class="pun">.</span><span class="pln">name</span><span class="pun">}}</span><span class="pln">
  </span><span class="pun">&lt;/</span><span class="pln">div</span><span class="pun">&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">和模板相伴的组件类可以提供英雄数组，能把新的英雄添加到数组中，还能重置英雄数组。</p><p translation-origin="off">The companion component class provides heroes, adds heroes into the array, and can reset the array.</p><code-example path="pipes/src/app/flying-heroes.component.ts" region="v1" header="src/app/flying-heroes.component.ts (v1)" ng-version="9.0.0-rc.11"><div style="display:none">export class FlyingHeroesComponent { heroes: any[] = []; canFly = true; constructor() { this.reset(); } addHero(name: string) { name = name.trim(); if (!name) { return; } let hero = {name, canFly: this.canFly}; this.heroes.push(hero); } reset() { this.heroes = HEROES.slice(); } }</div><header class="ng-star-inserted">src/app/flying-heroes.component.ts (v1)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.component.ts (v1)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">FlyingHeroesComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  heroes</span><span class="pun">:</span><span class="pln"> any</span><span class="pun">[]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[];</span><span class="pln">
  canFly </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">true</span><span class="pun">;</span><span class="pln">
  </span><span class="kwd">constructor</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">reset</span><span class="pun">();</span><span class="pln"> </span><span class="pun">}</span><span class="pln">

  addHero</span><span class="pun">(</span><span class="pln">name</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">string</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    name </span><span class="pun">=</span><span class="pln"> name</span><span class="pun">.</span><span class="pln">trim</span><span class="pun">();</span><span class="pln">
    </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(!</span><span class="pln">name</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">return</span><span class="pun">;</span><span class="pln"> </span><span class="pun">}</span><span class="pln">
    </span><span class="kwd">let</span><span class="pln"> hero </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="pln">name</span><span class="pun">,</span><span class="pln"> canFly</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">canFly</span><span class="pun">};</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes</span><span class="pun">.</span><span class="pln">push</span><span class="pun">(</span><span class="pln">hero</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

  reset</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes </span><span class="pun">=</span><span class="pln"> HEROES</span><span class="pun">.</span><span class="pln">slice</span><span class="pun">();</span><span class="pln"> </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">你可以添加新的英雄，加完之后，Angular 就会更新显示。 <code>reset</code> 按钮会把 <code>heroes</code> 替换成一个由原来的英雄组成的新数组，重置完之后，Angular 就会更新显示。 如果你提供了删除或修改英雄的能力，Angular 也会检测到那些更改，并更新显示。</p><p translation-origin="off">You can add heroes and Angular updates the display when you do. If you click the <code>reset</code> button, Angular replaces <code>heroes</code> with a new array of the original heroes and updates the display. If you added the ability to remove or change a hero, Angular would detect those changes and update the display as well.</p><h3 class="no-toc" id="flyingheroespipe" translation-result="on"><i>“会飞的英雄”管道（FlyingHeroesPipe）</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#flyingheroespipe"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="flyingheroespipe"><i>FlyingHeroesPipe</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#flyingheroespipe"><i class="material-icons">link</i></a></h3><p translation-result="on">往 <code>*<a href="api/common/NgForOf" class="code-anchor">ngFor</a></code> 重复器中添加一个 <code>FlyingHeroesPipe</code> 管道，这个管道能过滤出所有会飞的英雄。</p><p translation-origin="off">Add a <code>FlyingHeroesPipe</code> to the <code>*<a href="api/common/NgForOf" class="code-anchor">ngFor</a></code> repeater that filters the list of heroes to just those heroes who can fly.</p><code-example path="pipes/src/app/flying-heroes.component.html" region="template-flying-heroes" header="src/app/flying-heroes.component.html (flyers)" ng-version="9.0.0-rc.11"><div style="display:none">&lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>="let hero of (heroes | flyingHeroes)"&gt; {{hero.name}} &lt;/div&gt;</div><header class="ng-star-inserted">src/app/flying-heroes.component.html (flyers)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.component.html (flyers)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="tag">&lt;div</span><span class="pln"> *</span><a href="api/common/NgForOf" class="code-anchor"><span class="atn">ngFor</span></a><span class="pun">=</span><span class="atv">"let hero of (heroes | flyingHeroes)"</span><span class="tag">&gt;</span><span class="pln">
  {{hero.name}}
</span><span class="tag">&lt;/div&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">下面是 <code>FlyingHeroesPipe</code> 的实现，它遵循了以前讲过的那些写自定义管道的模式。</p><p translation-origin="off">Here's the <code>FlyingHeroesPipe</code> implementation, which follows the pattern for custom pipes described earlier.</p><code-example path="pipes/src/app/flying-heroes.pipe.ts" region="pure" header="src/app/flying-heroes.pipe.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Pipe" class="code-anchor">Pipe</a>, <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> } from '@angular/core'; import { Flyer } from './heroes'; @<a href="api/core/Pipe" class="code-anchor">Pipe</a>({ name: 'flyingHeroes' }) export class FlyingHeroesPipe implements <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> { transform(allHeroes: Flyer[]) { return allHeroes.filter(hero =&gt; hero.canFly); } }</div><header class="ng-star-inserted">src/app/flying-heroes.pipe.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.pipe.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Pipe" class="code-anchor"><span class="typ">Pipe</span></a><span class="pun">,</span><span class="pln"> </span><a href="api/core/PipeTransform" class="code-anchor"><span class="typ">PipeTransform</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Flyer</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./heroes'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Pipe" class="code-anchor"><span class="lit">Pipe</span></a><span class="pun">({</span><span class="pln"> name</span><span class="pun">:</span><span class="pln"> </span><span class="str">'flyingHeroes'</span><span class="pln"> </span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">FlyingHeroesPipe</span><span class="pln"> </span><span class="kwd">implements</span><span class="pln"> </span><a href="api/core/PipeTransform" class="code-anchor"><span class="typ">PipeTransform</span></a><span class="pln"> </span><span class="pun">{</span><span class="pln">
  transform</span><span class="pun">(</span><span class="pln">allHeroes</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Flyer</span><span class="pun">[])</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">return</span><span class="pln"> allHeroes</span><span class="pun">.</span><span class="pln">filter</span><span class="pun">(</span><span class="pln">hero </span><span class="pun">=&gt;</span><span class="pln"> hero</span><span class="pun">.</span><span class="pln">canFly</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">当运行<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>时，你看到一种奇怪的行为。添加的每个英雄都是会飞行的英雄，但是没有一个被显示出来。</p><p translation-origin="off">Notice the odd behavior in the<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>: when you add flying heroes, none of them are displayed under "Heroes who fly."</p><p translation-result="on">虽然你没有得到期望的行为，但 Angular 也没有出错。 这里只是用了另一种变更检测算法 —— 它会忽略对列表及其子项所做的任何更改。</p><p translation-origin="off">Although you're not getting the behavior you want, Angular isn't broken. It's just using a different change-detection algorithm that ignores changes to the list or any of its items.</p><p translation-result="on">注意这里是如何添加新英雄的：</p><p translation-origin="off">Notice how a hero is added:</p><code-example path="pipes/src/app/flying-heroes.component.ts" region="push" header="src/app/flying-heroes.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">this.heroes.push(hero);</div><header class="ng-star-inserted">src/app/flying-heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes</span><span class="pun">.</span><span class="pln">push</span><span class="pun">(</span><span class="pln">hero</span><span class="pun">);</span></code>
    </pre></aio-code></code-example><p translation-result="on">当你往 <code>heroes</code> 数组中添加一个新的英雄时，这个数组的引用并没有改变。它还是那个数组。而引用却是 Angular 所关心的一切。 在它看来，<em>这是同一个数组，没有变化，也就不需要更新显示</em>。</p><p translation-origin="off">You add the hero into the <code>heroes</code> array. The reference to the array hasn't changed. It's the same array. That's all Angular cares about. From its perspective, <em>same array, no change, no display update</em>.</p><p translation-result="on">要修复它，就要创建一个新数组，把这个英雄追加进去，并把它赋给 <code>heroes</code>。 这次，Angular 检测到数组的引用变化了。它执行了这个管道，并使用这个新数组更新显示，这次它就包括新的飞行英雄了。</p><p translation-origin="off">To fix that, create an array with the new hero appended and assign that to <code>heroes</code>. This time Angular detects that the array reference has changed. It executes the pipe and updates the display with the new array, which includes the new flying hero.</p><p translation-result="on">如果你<strong>修改了</strong>这个数组，没有管道被执行，也没有显示被更新。 如果你<strong>替换了</strong>这个数组，管道就会被执行，显示也更新了。 这个<em>飞行英雄</em>的例子用检查框和其它显示内容扩展了原有代码，来帮你体验这些效果。</p><p translation-origin="off">If you <em>mutate</em> the array, no pipe is invoked and the display isn't updated; if you <em>replace</em> the array, the pipe executes and the display is updated. The Flying Heroes application extends the code with checkbox switches and additional displays to help you experience these effects.</p><div class="lightbox"><img src="generated/images/guide/pipes/flying-heroes-anim.gif" alt="Flying Heroes" width="360" height="412"></div><p translation-result="on">直接替换这个数组是通知 Angular 更新显示的一种高效方式。 你该什么时候替换这个数组呢？当数据变化的时候。 在这个<em>玩具级</em>例子中，这是一个简单的规则，因为这里修改数据的唯一途径就是添加新英雄。</p><p translation-origin="off">Replacing the array is an efficient way to signal Angular to update the display. When do you replace the array? When the data changes. That's an easy rule to follow in <em>this</em> example where the only way to change the data is by adding a hero.</p><p translation-result="on">更多情况下，你不知道什么时候数据变化了，尤其是在那些有很多种途径改动数据的程序中 —— 可能在程序中很远的地方。 组件就是一个通常无法知道那些改动的例子。此外，它会导致削足适履 —— 扭曲组件的设计来适应管道。 要尽可能保持组件类独立于 HTML。组件不应该关心管道的存在。</p><p translation-origin="off">More often, you don't know when the data has changed, especially in applications that mutate data in many ways, perhaps in application locations far away. A component in such an application usually can't know about those changes. Moreover, it's unwise to distort the component design to accommodate a pipe. Strive to keep the component class independent of the HTML. The component should be unaware of pipes.</p><p translation-result="on">为了过滤出会飞的英雄，考虑使用<em>非纯(impure)管道</em>。</p><p translation-origin="off">For filtering flying heroes, consider an <em>impure pipe</em>.</p><h2 id="pure-and-impure-pipes" translation-result="on">纯(pure)管道与非纯(impure)管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pure-and-impure-pipes"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="pure-and-impure-pipes">Pure and impure pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pure-and-impure-pipes"><i class="material-icons">link</i></a></h2><p translation-result="on">有两类管道：<strong>纯</strong>的与<strong>非纯</strong>的。 默认情况下，管道都是纯的。以前见到的每个管道都是纯的。 通过把它的 <code>pure</code> 标志设置为 <code>false</code>，你可以制作一个非纯管道。你可以像这样让 <code>FlyingHeroesPipe</code> 变成非纯的：</p><p translation-origin="off">There are two categories of pipes: <em>pure</em> and <em>impure</em>. Pipes are pure by default. Every pipe you've seen so far has been pure. You make a pipe impure by setting its pure flag to false. You could make the <code>FlyingHeroesPipe</code> impure like this:</p><code-example path="pipes/src/app/flying-heroes.pipe.ts" region="pipe-decorator" header="src/app/flying-heroes.pipe.ts" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Pipe" class="code-anchor">Pipe</a>({ name: 'flyingHeroesImpure', pure: false })</div><header class="ng-star-inserted">src/app/flying-heroes.pipe.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.pipe.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Pipe" class="code-anchor"><span class="lit">Pipe</span></a><span class="pun">({</span><span class="pln">
  name</span><span class="pun">:</span><span class="pln"> </span><span class="str">'flyingHeroesImpure'</span><span class="pun">,</span><span class="pln">
  pure</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">false</span><span class="pln">
</span><span class="pun">})</span></code>
    </pre></aio-code></code-example><p translation-result="on">在继续往下走之前，先理解一下<em>纯</em>和<em>非纯</em>之间的区别，从<em>纯</em>管道开始。</p><p translation-origin="off">Before doing that, understand the difference between pure and impure, starting with a pure pipe.</p><h3 class="no-toc" id="pure-pipes" translation-result="on">纯管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pure-pipes"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="pure-pipes">Pure pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pure-pipes"><i class="material-icons">link</i></a></h3><p translation-result="on">Angular 只有在它检测到输入值发生了<em>纯变更</em>时才会执行<em>纯管道</em>。 <strong><em>纯变更</em></strong>是指对原始类型值(<code>String</code>、<code>Number</code>、<code>Boolean</code>、<code><a href="" class="code-anchor">Symbol</a></code>)的更改， 或者对对象引用(<code>Date</code>、<code>Array</code>、<code>Function</code>、<code>Object</code>)的更改。</p><p translation-origin="off">Angular executes a <em>pure pipe</em> only when it detects a <em>pure change</em> to the input value. A pure change is either a change to a primitive input value (<code>String</code>, <code>Number</code>, <code>Boolean</code>, <code><a href="" class="code-anchor">Symbol</a></code>) or a changed object reference (<code>Date</code>, <code>Array</code>, <code>Function</code>, <code>Object</code>).</p><p translation-result="on">Angular 会忽略(复合)对象<em>内部</em>的更改。 如果你更改了输入日期(<code>Date</code>)中的月份、往一个输入数组(<code>Array</code>)中添加新值或者更新了一个输入对象(<code>Object</code>)的属性，它都不会调用纯管道。</p><p translation-origin="off">Angular ignores changes within (composite) objects. It won't call a pure pipe if you change an input month, add to an input array, or update an input object property.</p><p translation-result="on">这可能看起来是一种限制，但它保证了速度。 对象引用的检查是非常快的(比递归的深检查要快得多)，所以 Angular 可以快速的决定是否应该跳过管道执行和视图更新。</p><p translation-origin="off">This may seem restrictive but it's also fast. An object reference check is fast—much faster than a deep check for differences—so Angular can quickly determine if it can skip both the pipe execution and a view update.</p><p translation-result="on">因此，如果要和变更检测策略打交道，就会更喜欢用纯管道。 如果不能，你就<em>可以</em>转回到非纯管道。</p><p translation-origin="off">For this reason, a pure pipe is preferable when you can live with the change detection strategy. When you can't, you <em>can</em> use the impure pipe.</p><div class="alert is-helpful"><p translation-result="on">或者你也可以完全不用管道。 有时候，使用组件的属性能比用管道更好的达到目的，后面会再讨论这一点。</p><p translation-origin="off">Or you might not use a pipe at all. It may be better to pursue the pipe's purpose with a property of the component, a point that's discussed later in this page.</p></div><h3 class="no-toc" id="impure-pipes" translation-result="on">非纯管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#impure-pipes"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="impure-pipes">Impure pipes<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#impure-pipes"><i class="material-icons">link</i></a></h3><p translation-result="on">Angular 会在每个组件的变更检测周期中执行<em>非纯管道</em>。 非纯管道可能会被调用很多次，和每个按键或每次鼠标移动一样频繁。</p><p translation-origin="off">Angular executes an <em>impure pipe</em> during every component change detection cycle. An impure pipe is called often, as often as every keystroke or mouse-move.</p><p translation-result="on">要在脑子里绷着这根弦，必须小心翼翼的实现非纯管道。 一个昂贵、迟钝的管道将摧毁用户体验。</p><p translation-origin="off">With that concern in mind, implement an impure pipe with great care. An expensive, long-running pipe could destroy the user experience.</p><a id="impure-flying-heroes"></a><h3 class="no-toc" id="an-impure-flyingheroespipe" translation-result="on">非纯管道 <i>FlyingHeroesPipe</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#an-impure-flyingheroespipe"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="an-impure-flyingheroespipe">An impure <i>FlyingHeroesPipe</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#an-impure-flyingheroespipe"><i class="material-icons">link</i></a></h3><p translation-result="on">把 <code>FlyingHeroesPipe</code> 换成了 <code>FlyingHeroesImpurePipe</code>。 下面是完整的实现：</p><p translation-origin="off">A flip of the switch turns the <code>FlyingHeroesPipe</code> into a <code>FlyingHeroesImpurePipe</code>. The complete implementation is as follows:</p><code-tabs ng-version="9.0.0-rc.11"><div style="display:none"><code-pane header="FlyingHeroesImpurePipe" path="pipes/src/app/flying-heroes.pipe.ts" region="impure">@<a href="api/core/Pipe" class="code-anchor">Pipe</a>({ name: 'flyingHeroesImpure', pure: false }) export class FlyingHeroesImpurePipe extends FlyingHeroesPipe {}</code-pane><code-pane header="FlyingHeroesPipe" path="pipes/src/app/flying-heroes.pipe.ts" region="pure">import { <a href="api/core/Pipe" class="code-anchor">Pipe</a>, <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> } from '@angular/core'; import { Flyer } from './heroes'; @<a href="api/core/Pipe" class="code-anchor">Pipe</a>({ name: 'flyingHeroes' }) export class FlyingHeroesPipe implements <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> { transform(allHeroes: Flyer[]) { return allHeroes.filter(hero =&gt; hero.canFly); } }</code-pane></div><mat-card class="mat-card"><mat-tab-group class="mat-tab-group code-tab-group mat-primary"><mat-tab-header class="mat-tab-header"><div aria-hidden="true" mat-ripple="" class="mat-ripple mat-tab-header-pagination mat-tab-header-pagination-before mat-elevation-z4 mat-tab-header-pagination-disabled"><div class="mat-tab-header-pagination-chevron"></div></div><div class="mat-tab-label-container"><div role="tablist" class="mat-tab-list" style="transform:translateX(0)"><div class="mat-tab-labels"><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label mat-tab-label-active ng-star-inserted" id="mat-tab-label-0-0" tabindex="0" aria-posinset="1" aria-setsize="2" aria-controls="mat-tab-content-0-0" aria-selected="true" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">FlyingHeroesImpurePipe</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-0-1" tabindex="-1" aria-posinset="2" aria-setsize="2" aria-controls="mat-tab-content-0-1" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">FlyingHeroesPipe</span></div></div></div><mat-ink-bar class="mat-ink-bar" style="visibility:visible;left:0;width:202px"></mat-ink-bar></div></div><div aria-hidden="true" mat-ripple="" class="mat-ripple mat-tab-header-pagination mat-tab-header-pagination-after mat-elevation-z4 mat-tab-header-pagination-disabled"><div class="mat-tab-header-pagination-chevron"></div></div></mat-tab-header><div class="mat-tab-body-wrapper"><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-2 mat-tab-body-active ng-star-inserted" id="mat-tab-content-0-0" aria-labelledby="mat-tab-label-0-0"><div class="mat-tab-body-content ng-tns-c50-2 ng-trigger ng-trigger-translateTab" style="transform:none"><aio-code class="ng-star-inserted" style=""><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from FlyingHeroesImpurePipe">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Pipe" class="code-anchor"><span class="lit">Pipe</span></a><span class="pun">({</span><span class="pln">
  name</span><span class="pun">:</span><span class="pln"> </span><span class="str">'flyingHeroesImpure'</span><span class="pun">,</span><span class="pln">
  pure</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">false</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">FlyingHeroesImpurePipe</span><span class="pln"> </span><span class="kwd">extends</span><span class="pln"> </span><span class="typ">FlyingHeroesPipe</span><span class="pln"> </span><span class="pun">{}</span></code>
    </pre></aio-code></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-3 ng-star-inserted" id="mat-tab-content-0-1" aria-labelledby="mat-tab-label-0-1"><div class="mat-tab-body-content ng-tns-c50-3 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body></div></mat-tab-group></mat-card></code-tabs><p translation-result="on">你把它从 <code>FlyingHeroesPipe</code> 中继承下来，以证明无需改动内部代码。 唯一的区别是管道元数据中的 <code>pure</code> 标志。</p><p translation-origin="off">You inherit from <code>FlyingHeroesPipe</code> to prove the point that nothing changed internally. The only difference is the <code>pure</code> flag in the pipe metadata.</p><p translation-result="on">这是一个很好地非纯管道候选者，因为它的 <code>transform</code> 函数又小又快。</p><p translation-origin="off">This is a good candidate for an impure pipe because the <code>transform</code> function is trivial and fast.</p><code-example path="pipes/src/app/flying-heroes.pipe.ts" header="src/app/flying-heroes.pipe.ts (filter)" region="filter" ng-version="9.0.0-rc.11"><div style="display:none">return allHeroes.filter(hero =&gt; hero.canFly);</div><header class="ng-star-inserted">src/app/flying-heroes.pipe.ts (filter)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes.pipe.ts (filter)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">return</span><span class="pln"> allHeroes</span><span class="pun">.</span><span class="pln">filter</span><span class="pun">(</span><span class="pln">hero </span><span class="pun">=&gt;</span><span class="pln"> hero</span><span class="pun">.</span><span class="pln">canFly</span><span class="pun">);</span></code>
    </pre></aio-code></code-example><p translation-result="on">你可以从 <code>FlyingHeroesComponent</code> 派生出一个 <code>FlyingHeroesImpureComponent</code>。</p><p translation-origin="off">You can derive a <code>FlyingHeroesImpureComponent</code> from <code>FlyingHeroesComponent</code>.</p><code-example path="pipes/src/app/flying-heroes-impure.component.html" header="src/app/flying-heroes-impure.component.html (excerpt)" region="template-flying-heroes" ng-version="9.0.0-rc.11"><div style="display:none">&lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>="let hero of (heroes | flyingHeroesImpure)"&gt; {{hero.name}} &lt;/div&gt;</div><header class="ng-star-inserted">src/app/flying-heroes-impure.component.html (excerpt)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/flying-heroes-impure.component.html (excerpt)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="tag">&lt;div</span><span class="pln"> *</span><a href="api/common/NgForOf" class="code-anchor"><span class="atn">ngFor</span></a><span class="pun">=</span><span class="atv">"let hero of (heroes | flyingHeroesImpure)"</span><span class="tag">&gt;</span><span class="pln">
  {{hero.name}}
</span><span class="tag">&lt;/div&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">唯一的重大改动就是管道。 你可以在<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>中确认，当你添加新的英雄甚至修改 <code>heroes</code> 数组时，这个<em>会飞的英雄</em>的显示也跟着更新了。</p><p translation-origin="off">The only substantive change is the pipe in the template. You can confirm in the<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="现场演练" href="generated/live-examples/pipes/stackblitz.html">现场演练</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/pipes/pipes.zip">下载范例</a></span></span></span></live-example>that the <em>flying heroes</em> display updates as you add heroes, even when you mutate the <code>heroes</code> array.</p><a id="async-pipe"></a><h3 class="no-toc" id="the-impure-asyncpipe" translation-result="on">非纯 <i>AsyncPipe</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#the-impure-asyncpipe"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="the-impure-asyncpipe">The impure <i>AsyncPipe</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#the-impure-asyncpipe"><i class="material-icons">link</i></a></h3><p translation-result="on">Angular 的 <code><a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a></code> 是一个有趣的非纯管道的例子。 <code><a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a></code> 接受一个 <code>Promise</code> 或 <code>Observable</code> 作为输入，并且自动订阅这个输入，最终返回它们给出的值。</p><p translation-origin="off">The Angular <code><a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a></code> is an interesting example of an impure pipe. The <code><a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a></code> accepts a <code>Promise</code> or <code>Observable</code> as input and subscribes to the input automatically, eventually returning the emitted values.</p><p translation-result="on"><code><a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a></code> 管道是有状态的。 该管道维护着一个所输入的 <code>Observable</code> 的订阅，并且持续从那个 <code>Observable</code> 中发出新到的值。</p><p translation-origin="off">The <code><a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a></code> is also stateful. The pipe maintains a subscription to the input <code>Observable</code> and keeps delivering values from that <code>Observable</code> as they arrive.</p><p translation-result="on">下面例子使用该 <code><a href="api/core/testing/async" class="code-anchor">async</a></code> 管道把一个消息字符串(<code><a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>$</code>)的 <code>Observable</code> 绑定到视图中。</p><p translation-origin="off">This next example binds an <code>Observable</code> of message strings (<code><a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>$</code>) to a view with the <code><a href="api/core/testing/async" class="code-anchor">async</a></code> pipe.</p><code-example path="pipes/src/app/hero-async-message.component.ts" header="src/app/hero-async-message.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Component" class="code-anchor">Component</a> } from '@angular/core'; import { Observable, interval } from 'rxjs'; import { map, take } from 'rxjs/operators'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-hero-message', template: ` &lt;h2&gt;Async Hero Message and <a href="api/common/AsyncPipe" class="code-anchor">AsyncPipe</a>&lt;/h2&gt; &lt;p&gt;Message: {{ <a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>$ | <a href="api/core/testing/async" class="code-anchor">async</a> }}&lt;/p&gt; &lt;button (click)="resend()"&gt;Resend&lt;/button&gt;`, }) export class HeroAsyncMessageComponent { <a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>$: Observable&lt;string&gt;; private <a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a> = [ 'You are my hero!', 'You are the best hero!', 'Will you be my hero?' ]; constructor() { this.resend(); } resend() { this.message$ = interval(500).pipe( map(i =&gt; this.messages[i]), take(this.messages.length) ); } }</div><header class="ng-star-inserted">src/app/hero-async-message.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero-async-message.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Component" class="code-anchor"><span class="typ">Component</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Observable</span><span class="pun">,</span><span class="pln"> interval </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'rxjs'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> map</span><span class="pun">,</span><span class="pln"> take </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'rxjs/operators'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-hero-message'</span><span class="pun">,</span><span class="pln">
  </span><span class="kwd">template</span><span class="pun">:</span><span class="pln"> </span><span class="str">`
    &lt;h2&gt;Async Hero Message and </span><a href="api/common/AsyncPipe" class="code-anchor"><span class="str">AsyncPipe</span></a><span class="str">&lt;/h2&gt;
    &lt;p&gt;Message: {{ </span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="str">message</span></a><span class="str">$ | </span><a href="api/core/testing/async" class="code-anchor"><span class="str">async</span></a><span class="str"> }}&lt;/p&gt;
    &lt;button (click)="resend()"&gt;Resend&lt;/button&gt;`</span><span class="pun">,</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroAsyncMessageComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="pln">message</span></a><span class="pln">$</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Observable</span><span class="str">&lt;string&gt;</span><span class="pun">;</span><span class="pln">

  </span><span class="kwd">private</span><span class="pln"> </span><a href="api/service-worker/SwPush#messages" class="code-anchor"><span class="pln">messages</span></a><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[</span><span class="pln">
    </span><span class="str">'You are my hero!'</span><span class="pun">,</span><span class="pln">
    </span><span class="str">'You are the best hero!'</span><span class="pun">,</span><span class="pln">
    </span><span class="str">'Will you be my hero?'</span><span class="pln">
  </span><span class="pun">];</span><span class="pln">

  </span><span class="kwd">constructor</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">resend</span><span class="pun">();</span><span class="pln"> </span><span class="pun">}</span><span class="pln">

  resend</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">message$ </span><span class="pun">=</span><span class="pln"> interval</span><span class="pun">(</span><span class="lit">500</span><span class="pun">).</span><span class="pln">pipe</span><span class="pun">(</span><span class="pln">
      map</span><span class="pun">(</span><span class="pln">i </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messages</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]),</span><span class="pln">
      take</span><span class="pun">(</span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messages</span><span class="pun">.</span><span class="pln">length</span><span class="pun">)</span><span class="pln">
    </span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">这个 Async 管道节省了组件的样板代码。 组件不用订阅这个异步数据源，而且不用在被销毁时取消订阅(如果订阅了而忘了反订阅容易导致隐晦的内存泄露)。</p><p translation-origin="off">The Async pipe saves boilerplate in the component code. The component doesn't have to subscribe to the async data source, extract the resolved values and expose them for binding, and have to unsubscribe when it's destroyed (a potent source of memory leaks).</p><h3 class="no-toc" id="an-impure-caching-pipe" translation-result="on">一个非纯而且带缓存的管道<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#an-impure-caching-pipe"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="an-impure-caching-pipe">An impure caching pipe<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#an-impure-caching-pipe"><i class="material-icons">link</i></a></h3><p translation-result="on">来写更多的非纯管道：一个向服务器发起 HTTP 请求的管道。</p><p translation-origin="off">Write one more impure pipe, a pipe that makes an HTTP request.</p><p translation-result="on">时刻记住，非纯管道可能每隔几微秒就会被调用一次。 如果你不小心点，这个管道就会发起一大堆请求“攻击”服务器。</p><p translation-origin="off">Remember that impure pipes are called every few milliseconds. If you're not careful, this pipe will punish the server with requests.</p><p translation-result="on">下面这个管道只有当所请求的 URL 发生变化时才会向服务器发起请求。它会缓存服务器的响应。 代码如下，它使用<a href="guide/http">Angular http</a>客户端来接收数据</p><p translation-origin="off">In the following code, the pipe only calls the server when the requested URL changes and it caches the server response. The code uses the <a href="guide/http">Angular http</a> client to retrieve data:</p><code-example path="pipes/src/app/fetch-json.pipe.ts" header="src/app/fetch-json.pipe.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/common/http/HttpClient" class="code-anchor">HttpClient</a> } from '@angular/common/<a href="api/common/http" class="code-anchor">http</a>'; import { <a href="api/core/Pipe" class="code-anchor">Pipe</a>, <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> } from '@angular/core'; @<a href="api/core/Pipe" class="code-anchor">Pipe</a>({ name: 'fetch', pure: false }) export class FetchJsonPipe implements <a href="api/core/PipeTransform" class="code-anchor">PipeTransform</a> { private cachedData: any = null; private cachedUrl = ''; constructor(private <a href="api/common/http" class="code-anchor">http</a>: <a href="api/common/http/HttpClient" class="code-anchor">HttpClient</a>) { } transform(url: string): any { if (url !== this.cachedUrl) { this.cachedData = null; this.cachedUrl = url; this.http.get(url).subscribe(result =&gt; this.cachedData = result); } return this.cachedData; } }</div><header class="ng-star-inserted">src/app/fetch-json.pipe.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/fetch-json.pipe.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/common/http/HttpClient" class="code-anchor"><span class="typ">HttpClient</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln">          </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/common/</span><a href="api/common/http" class="code-anchor"><span class="str">http</span></a><span class="str">'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Pipe" class="code-anchor"><span class="typ">Pipe</span></a><span class="pun">,</span><span class="pln"> </span><a href="api/core/PipeTransform" class="code-anchor"><span class="typ">PipeTransform</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Pipe" class="code-anchor"><span class="lit">Pipe</span></a><span class="pun">({</span><span class="pln">
  name</span><span class="pun">:</span><span class="pln"> </span><span class="str">'fetch'</span><span class="pun">,</span><span class="pln">
  pure</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">false</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">FetchJsonPipe</span><span class="pln"> </span><span class="kwd">implements</span><span class="pln"> </span><a href="api/core/PipeTransform" class="code-anchor"><span class="typ">PipeTransform</span></a><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">private</span><span class="pln"> cachedData</span><span class="pun">:</span><span class="pln"> any </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">;</span><span class="pln">
  </span><span class="kwd">private</span><span class="pln"> cachedUrl </span><span class="pun">=</span><span class="pln"> </span><span class="str">''</span><span class="pun">;</span><span class="pln">

  </span><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">private</span><span class="pln"> </span><a href="api/common/http" class="code-anchor"><span class="pln">http</span></a><span class="pun">:</span><span class="pln"> </span><a href="api/common/http/HttpClient" class="code-anchor"><span class="typ">HttpClient</span></a><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span><span class="pln">

  transform</span><span class="pun">(</span><span class="pln">url</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">string</span><span class="pun">):</span><span class="pln"> any </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">url </span><span class="pun">!==</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">cachedUrl</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">cachedData </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">;</span><span class="pln">
      </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">cachedUrl </span><span class="pun">=</span><span class="pln"> url</span><span class="pun">;</span><span class="pln">
      </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">http</span><span class="pun">.</span><span class="kwd">get</span><span class="pun">(</span><span class="pln">url</span><span class="pun">).</span><span class="pln">subscribe</span><span class="pun">(</span><span class="pln">result </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">cachedData </span><span class="pun">=</span><span class="pln"> result</span><span class="pun">);</span><span class="pln">
    </span><span class="pun">}</span><span class="pln">

    </span><span class="kwd">return</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">cachedData</span><span class="pun">;</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">接下来在一个测试挽具组件中演示一下它，该组件的模板中定义了两个使用到此管道的绑定，它们都从 <code>heroes.json</code> 文件中取得英雄数据。</p><p translation-origin="off">Now demonstrate it in a harness component whose template defines two bindings to this pipe, both requesting the heroes from the <code>heroes.json</code> file.</p><code-example path="pipes/src/app/hero-list.component.ts" header="src/app/hero-list.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Component" class="code-anchor">Component</a> } from '@angular/core'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-hero-list', template: ` &lt;h2&gt;Heroes from JSON File&lt;/h2&gt; &lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>="let hero of ('assets/heroes.json' | fetch) "&gt; {{hero.name}} &lt;/div&gt; &lt;p&gt;Heroes as JSON: {{'assets/heroes.json' | fetch | <a href="api/common/JsonPipe" class="code-anchor">json</a>}} &lt;/p&gt;` }) export class HeroListComponent { }</div><header class="ng-star-inserted">src/app/hero-list.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero-list.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Component" class="code-anchor"><span class="typ">Component</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-hero-list'</span><span class="pun">,</span><span class="pln">
  </span><span class="kwd">template</span><span class="pun">:</span><span class="pln"> </span><span class="str">`
    &lt;h2&gt;Heroes from JSON File&lt;/h2&gt;

    &lt;div *</span><a href="api/common/NgForOf" class="code-anchor"><span class="str">ngFor</span></a><span class="str">="let hero of ('assets/heroes.json' | fetch) "&gt;
      {{hero.name}}
    &lt;/div&gt;

    &lt;p&gt;Heroes as JSON:
      {{'assets/heroes.json' | fetch | </span><a href="api/common/JsonPipe" class="code-anchor"><span class="str">json</span></a><span class="str">}}
    &lt;/p&gt;`</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroListComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">组件渲染起来是这样的：</p><p translation-origin="off">The component renders as the following:</p><div class="lightbox"><img src="generated/images/guide/pipes/hero-list.png" alt="Hero List" width="400" height="232"></div><p translation-result="on">这个管道上的断点请求数据的过程显示：</p><p translation-origin="off">A breakpoint on the pipe's request for data shows the following:</p><ul><li><p translation-result="on">每个绑定都有它自己的管道实例。</p><p translation-origin="off">Each binding gets its own pipe instance.</p></li><li><p translation-result="on">每个管道实例都缓存了它自己的 URL 和数据。</p><p translation-origin="off">Each pipe instance caches its own URL and data.</p></li><li><p translation-result="on">每个管道实例都只调用一次服务器。</p><p translation-origin="off">Each pipe instance only calls the server once.</p></li></ul><h3 class="no-toc" id="jsonpipe"><i>JsonPipe</i><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#jsonpipe"><i class="material-icons">link</i></a></h3><p translation-result="on">第二个绑定除了用到 <code>FetchPipe</code> 之外还链接了更多管道。 它通过串联上内置管道 <code><a href="api/common/JsonPipe" class="code-anchor">JsonPipe</a></code> 来把英雄数据显示成了 JSON 格式。</p><p translation-origin="off">In the previous code sample, the second <code>fetch</code> pipe binding demonstrates more pipe chaining. It displays the same hero data in JSON format by chaining through to the built-in <code><a href="api/common/JsonPipe" class="code-anchor">JsonPipe</a></code>.</p><div class="callout is-helpful"><header translation-result="on">借助 json 管道进行调试</header><header translation-origin="off">Debugging with the json pipe</header><p translation-result="on"><a href="api/common/JsonPipe">JsonPipe</a>为你诊断数据绑定的某些神秘错误或为做进一步绑定而探查数据时，提供了一个简单途径。</p><p translation-origin="off">The <a href="api/common/JsonPipe">JsonPipe</a> provides an easy way to diagnose a mysteriously failing data binding or inspect an object for future binding.</p></div><a id="pure-pipe-pure-fn"></a><h3 class="no-toc" id="pure-pipes-and-pure-functions" translation-result="on">纯管道与纯函数<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pure-pipes-and-pure-functions"><i class="material-icons">link</i></a></h3><h3 class="no-toc" translation-origin="off" id="pure-pipes-and-pure-functions">Pure pipes and pure functions<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#pure-pipes-and-pure-functions"><i class="material-icons">link</i></a></h3><p translation-result="on">纯管道使用纯函数。 纯函数是指在处理输入并返回结果时，不会产生任何副作用的函数。 给定相同的输入，它们总是返回相同的输出。</p><p translation-origin="off">A pure pipe uses pure functions. Pure functions process inputs and return values without detectable side effects. Given the same input, they should always return the same output.</p><p translation-result="on">在本章前面讨论的管道都是用纯函数实现的。 内置的 <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code> 就是一个用纯函数实现的纯管道。 <code>ExponentialStrengthPipe</code> 是如此， <code>FlyingHeroesComponent</code> 也是如此。 不久前你刚看过的 <code>FlyingHeroesImpurePipe</code> 就是一个<em>用纯函数实现的非纯管道</em>。</p><p translation-origin="off">The pipes discussed earlier in this page are implemented with pure functions. The built-in <code><a href="api/common/DatePipe" class="code-anchor">DatePipe</a></code> is a pure pipe with a pure function implementation. So are the <code>ExponentialStrengthPipe</code> and <code>FlyingHeroesPipe</code>. A few steps back, you reviewed the <code>FlyingHeroesImpurePipe</code>—an impure pipe with a pure function.</p><p translation-result="on">但是一个<em>纯管道</em>必须总是用<em>纯函数</em>实现。忽略这个警告将导致失败并带来一大堆这样的控制台错误：表达式在被检查后被变更。</p><p translation-origin="off">But always implement a <em>pure pipe</em> with a <em>pure function</em>. Otherwise, you'll see many console errors regarding expressions that changed after they were checked.</p><h2 id="next-steps" translation-result="on">下一步<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#next-steps"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="next-steps">Next steps<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#next-steps"><i class="material-icons">link</i></a></h2><p translation-result="on">管道能很好的封装和共享的通用“值-显示”转换逻辑。可以像样式一样使用它们，把它们扔到模板表达式中，以提升视图的表现力和可用性。</p><p translation-origin="off">Pipes are a great way to encapsulate and share common display-value transformations. Use them like styles, dropping them into your template's expressions to enrich the appeal and usability of your views.</p><p translation-result="on">要浏览 Angular 的所有内置管道，请到<a href="api?type=pipe">API 参考手册</a>。 学着写写自定义管道，并贡献给开发社区。</p><p translation-origin="off">Explore Angular's inventory of built-in pipes in the <a href="api?type=pipe">API Reference</a>. Try writing a custom pipe and perhaps contributing it to the community.</p><a id="no-filter-pipe"></a><h2 id="appendix-no-filterpipe-or-orderbypipe" translation-result="on">附录：没有 <em>FilterPipe</em> 或者 <em>OrderByPipe</em><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#appendix-no-filterpipe-or-orderbypipe"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="appendix-no-filterpipe-or-orderbypipe">Appendix: No <em>FilterPipe</em> or <em>OrderByPipe</em><a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/pipes#appendix-no-filterpipe-or-orderbypipe"><i class="material-icons">link</i></a></h2><p translation-result="on">Angular 没有随身发布过滤或列表排序的管道。 熟悉 AngularJS 的开发人员应该知道 <code>filter</code> 和 <code>orderBy</code> 过滤器，但在 Angular 中它们没有等价物。</p><p translation-origin="off">Angular doesn't provide pipes for filtering or sorting lists. Developers familiar with AngularJS know these as <code>filter</code> and <code>orderBy</code>. There are no equivalents in Angular.</p><p translation-result="on">这并不是疏忽。Angular 不想提供这些管道，因为 (a) 它们性能堪忧，以及 (b) 它们会阻止比较激进的代码最小化(minification)。 无论是 <code>filter</code> 还是 <code>orderBy</code> 都需要它的参数引用对象型属性。 你在前面学过，这样的管道必然是<a href="guide/pipes#pure-and-impure-pipes"><em>非纯管道</em></a>，并且 Angular 会在几乎每一次变更检测周期中调用非纯管道。</p><p translation-origin="off">This isn't an oversight. Angular doesn't offer such pipes because they perform poorly and prevent aggressive minification. Both <code>filter</code> and <code>orderBy</code> require parameters that reference object properties. Earlier in this page, you learned that such pipes must be <a href="guide/pipes#pure-and-impure-pipes">impure</a> and that Angular calls impure pipes in almost every change-detection cycle.</p><p translation-result="on">过滤、 特别是排序是昂贵的操作。 当 Angular 每秒调用很多次这类管道函数时，即使是中等规模的列表都可能严重降低用户体验。 在 AngularJS 程序中，<code>filter</code> 和 <code>orderBy</code> 经常被误用，结果连累到 Angular 自身，人们抱怨说它太慢。 从某种意义上，这也不冤：谁叫 AngularJS 把 <code>filter</code> 和 <code>orderBy</code> 作为首发队员呢？是它自己准备了这个性能陷阱。</p><p translation-origin="off">Filtering and especially sorting are expensive operations. The user experience can degrade severely for even moderate-sized lists when Angular calls these pipe methods many times per second. <code>filter</code> and <code>orderBy</code> have often been abused in AngularJS apps, leading to complaints that Angular itself is slow. That charge is fair in the indirect sense that AngularJS prepared this performance trap by offering <code>filter</code> and <code>orderBy</code> in the first place.</p><p translation-result="on">虽然不是很明显，但代码最小化方面也存在风险。想象一个用于英雄列表的排序管道。该列表可能根据英雄原始属性中的 <code>name</code> 和 <code>planet</code> 进行排序，就像这样：</p><p translation-origin="off">The minification hazard is also compelling, if less obvious. Imagine a sorting pipe applied to a list of heroes. The list might be sorted by hero <code>name</code> and <code>planet</code> of origin properties in the following way:</p><code-example language="html" ng-version="9.0.0-rc.11"><div style="display:none">&lt;!-- NOT REAL CODE! --&gt; &lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>="let hero of heroes | orderBy:'name,planet'"&gt;&lt;/div&gt;</div><aio-code><pre class="lang-html prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="com">&lt;!-- NOT REAL CODE! --&gt;</span><span class="pln">
</span><span class="tag">&lt;div</span><span class="pln"> *</span><a href="api/common/NgForOf" class="code-anchor"><span class="atn">ngFor</span></a><span class="pun">=</span><span class="atv">"let hero of heroes | orderBy:'name,planet'"</span><span class="tag">&gt;&lt;/div&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">你使用文本字符串来标记出排序字段，期望管道通过索引形式(如 <code>hero['name']</code>)引用属性的值。 不幸的是，激进的代码最小化策略会<em>改变</em><code>Hero</code> 类的属性名，所以 <code>Hero.name</code> 和 <code>Hero.planet</code> 可能会被变成 <code>Hero.a</code> 和 <code>Hero.b</code>。 显然，<code>hero['name']</code> 是无法正常工作的。</p><p translation-origin="off">You identify the sort fields by text strings, expecting the pipe to reference a property value by indexing (such as <code>hero['name']</code>). Unfortunately, aggressive minification manipulates the <code>Hero</code> property names so that <code>Hero.name</code> and <code>Hero.planet</code> become something like <code>Hero.a</code> and <code>Hero.b</code>. Clearly <code>hero['name']</code> doesn't work.</p><p translation-result="on">然而有些人可能不想做那么激进的最小化， Angular 作为一个产品不应该拒绝那些想做激进的最小化的人。 所以，Angular 开发组决定随 Angular 一起发布的每样东西，都应该能被安全的最小化。</p><p translation-origin="off">While some may not care to minify this aggressively, the Angular product shouldn't prevent anyone from minifying aggressively. Therefore, the Angular team decided that everything Angular provides will minify safely.</p><p translation-result="on">Angular 开发组和一些有经验的 Angular 开发者强烈建议你：把你的过滤和排序逻辑挪进组件本身。 组件可以对外暴露一个 <code>filteredHeroes</code> 或 <code>sortedHeroes</code> 属性，这样它就获得控制权，以决定要用什么频度去执行其它辅助逻辑。 你原本准备实现为管道，并在整个应用中共享的那些功能，都能被改写为一个过滤/排序的服务，并注入到组件中。</p><p translation-origin="off">The Angular team and many experienced Angular developers strongly recommend moving filtering and sorting logic into the component itself. The component can expose a <code>filteredHeroes</code> or <code>sortedHeroes</code> property and take control over when and how often to execute the supporting logic. Any capabilities that you would have put in a pipe and shared across the app can be written in a filtering/sorting service and injected into the component.</p><p translation-result="on">如果你不需要顾虑这些性能和最小化问题，也可以创建自己的管道来实现这些功能(参考<a href="guide/pipes#impure-flying-heroes">FlyingHeroesPipe</a>中的写法)或到社区中去找找。</p><p translation-origin="off">If these performance and minification considerations don't apply to you, you can always create your own such pipes (similar to the <a href="guide/pipes#impure-flying-heroes">FlyingHeroesPipe</a>) or find them in the community.</p></div></div></aio-doc-viewer></main></mat-sidenav-content></mat-sidenav-container><div class="toc-container no-print ng-star-inserted"><aio-lazy-ce selector="aio-toc"><aio-toc ng-version="9.0.0-rc.11"><div class="toc-inner no-print collapsed ng-star-inserted"><ul class="toc-list"><li class="h1 ng-star-inserted active" title="管道"><a href="guide/pipes#pipes">管道</a></li><li class="h2 ng-star-inserted" title="使用管道"><a href="guide/pipes#using-pipes">使用管道</a></li><li class="h2 ng-star-inserted" title="内置的管道"><a href="guide/pipes#built-in-pipes">内置的管道</a></li><li class="h2 ng-star-inserted" title="对管道进行参数化"><a href="guide/pipes#parameterizing-a-pipe">对管道进行参数化</a></li><li class="h2 ng-star-inserted" title="链式管道"><a href="guide/pipes#chaining-pipes">链式管道</a></li><li class="h2 ng-star-inserted" title="自定义管道"><a href="guide/pipes#custom-pipes">自定义管道</a></li><li class="h2 ng-star-inserted" title="PipeTransform 接口"><a href="guide/pipes#the-pipetransform-interface"><em>PipeTransform</em> 接口</a></li><li class="h2 ng-star-inserted" title="能力倍增计算器"><a href="guide/pipes#power-boost-calculator">能力倍增计算器</a></li><li class="h2 ng-star-inserted" title="管道与变更检测"><a href="guide/pipes#pipes-and-change-detection">管道与变更检测</a></li><li class="h2 ng-star-inserted" title="纯(pure)管道与非纯(impure)管道"><a href="guide/pipes#pure-and-impure-pipes">纯(pure)管道与非纯(impure)管道</a></li><li class="h2 ng-star-inserted" title="下一步"><a href="guide/pipes#next-steps">下一步</a></li><li class="h2 ng-star-inserted" title="附录：没有 FilterPipe 或者 OrderByPipe"><a href="guide/pipes#appendix-no-filterpipe-or-orderbypipe">附录：没有 <em>FilterPipe</em> 或者 <em>OrderByPipe</em></a></li></ul></div></aio-toc></aio-lazy-ce></div><footer class="no-print"><aio-footer><div class="grid-fluid"><div class="footer-block ng-star-inserted"><h3>资源</h3><ul><li class="ng-star-inserted"><a class="link" href="about" title="Angular 贡献者。">关于</a></li><li class="ng-star-inserted"><a class="link" href="resources" title="网络上的 Angular 工具、培训、博客等">资源列表</a></li><li class="ng-star-inserted"><a class="link" href="presskit" title="我们的联系方式、LOGO 和品牌">宣传资料</a></li><li class="ng-star-inserted"><a class="link" href="https://blog.angular.io/" title="Angular 官方博客">博客</a></li><li class="ng-star-inserted"><a class="link" href="analytics" title="Angular 使用情况分析">使用情况分析</a></li></ul></div><div class="footer-block ng-star-inserted"><h3>帮助</h3><ul><li class="ng-star-inserted"><a 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